On Mon, 22 Jun 2026 16:43:35 -0400 Brian Daniels <[email protected]> wrote:
> From: Alexandre Courbot <[email protected]> > > Add the first version of the virtio-media driver. > > This driver acts roughly as a V4L2 relay between user-space and the > virtio virtual device on the host, so it is relatively simple, yet > unconventional. It doesn't use VB2 or other frameworks typically used in > a V4L2 driver, and most of its complexity resides in correctly and > efficiently building the virtio descriptor chain to pass to the host, > avoiding copies whenever possible. This is done by > scatterlist_builder.[ch]. > > This version supports MMAP buffers, while USERPTR buffers can also be > enabled through a driver option. DMABUF support is still pending. In practice, USERPTR was used on several drivers that wanted to share buffers between V4L2 and GPU (so, a previous approach before DMABUF implementation). On my tests with this driver, I was unable use a 1080p camera with V4L2 and GPU on crossvm. Lower resolutions worked. No idea if this was a limitation of crossvm (I only used it to test this driver) or if it is due to a poor MMAP implementation. > Compliance Testing > > This was tested using v4l2-compliance. Since virtio-media serves as > a proxy to host devices for the guest VMs, we expect the guest > compliance test to essentially match the host compliance test for the > same device. > > NOTE: v4l2-compliance changes its test behavior depending on the driver > name. In the guest, the driver name for virtio-media proxied-devices is > always "virtio-media", even if the actual host device has a driver name > of e.g. "uvcvideo". To ensure the test is consistent between the host > and the guest, I created a patch for the v4l2-compliance tool that > allows you to override the driver name. All test results that follow use > this patch: > https://lore.kernel.org/r/[email protected]/ As mentioned before, please submit this with their rationale in separate as a [PATCH v4l-utils] to linux-media ML. > > All tests used a Logitech USB Webcam C925e. Please test it displaying inside crossvm - or even better to QEMU if you manage to add virtio-media support to it. Being at QEMU makes a lot easier for everyone to test it. Thanks, Mauro
